1. Field of the Invention
The present invention relates generally to video signal processing apparatus and, more particularly to a video signal processing apparatus for use in a digital video tape recorder (digital VTR) which can realize special video effect processing or the like.
2. Description of the Prior Art
Digital video tape recorders or the like effect some proper signal processing on a reproduced video signal, such as an output phase of a reproduced signal or the like in order to realize special video effect processing. In such a digital VTR, an ancillary code such as a vertical interval time code (VITC code) is frequently inserted into the reproduced video signal. As is known, the VITC code is a time code which is inserted into an ancillary code area allocated to the period corresponding to the vertical blanking period (BLK period) such that the time code can be read out from the ancillary code area even in a variable speed playback mode.
When a video signal involving such ancillary code is reproduced and displayed on a picture screen of a monitor receiver, then a picture is displayed as shown in FIGS. 1A through 1C. The picture portion, which should be hidden by the blanking processing in actual practice, is represented in FIGS. 1A through 1C in order to gain a better understanding of the present invention.
FIG. 1A shows an example of a picture displayed on the picture screen before the output phase of the reproduced video signal is controlled. As shown in FIG. 1A, an ancillary area is hatched and vertical blanking areas are depicted by reference letters BLK. FIG. 1B shows an example of a picture displayed on the picture screen when a special effect processing is carried out by controlling the output phase of the video signal so as to shift a picture in the upward direction. By shifting the picture in the upper direction, the upper blanking area (BLK area) is erased from the picture screen. FIG. 1C shows an example of a picture displayed on the picture screen when a special effect processing is carried out by controlling the output phase of the video signal so as to shift a picture in the lower direction. In that case, the lower blanking area is erased from the picture screen.
The reason that the pictures are displayed as shown in FIGS. 1A through 1C will be described with reference to FIG. 2.
Referring to FIG. 2, when an area of exactly one picture screen from a reference point s is displayed, then the picture shown in FIG. 1A is presented. When the reference point is shifted (phase-shifted) from s to t, then the uppermost portion of the picture becomes the ancillary area and therefore the picture shown in FIG. 1B is presented. Further, when the video signal is phase-shifted so as to shift the reference point from s to u, then the blanking area in the uppermost portion of the picture screen is increased but the blanking area of the lowermost portion of the picture screen is cut, resulting in the picture being displayed as shown in FIG. 1C.
When the above-mentioned special effect processing is carried out, as is clear from FIG. 2, the phase shift of the output video signal is substantially equivalent to the phaseshift processing of the entirety of the video signal involving the ancillary area with the result that ancillary data inserting positions from the reference points s, t, u are changed with the phase-shift amount of the output phase. For this reason, the following problems arise:
In the video signal processing circuit such as the special effect processing circuit or the like, the above-mentioned ancillary data, e.g., VITC code, is extracted to obtain time code data in the variable speed playback mode, and this time code data must be transferred to a system controller or the like. To this end, a VITC code gate circuit is provided and the gate circuit generates a gating signal on the basis of the reference point s. Thus, when the reference point is phase-shifted by a phase-shift amount over one line such as from the reference point t or u, then the position of the gating signal is changed, which makes it impossible to correctly extract the VITC code.
If the output video signal thus phase-shifted is copied by another VTR by dubbing, for example, the position of the inserting line of the VITC code is changed so that the VITC code cannot be detected correctly, as described above.